1. Field of the Invention
The present invention relates to the determination of the location of a wireless device. More particularly, the present invention relates to the determination of the location of a wireless device with a hybrid system and method that utilizes BSS and NSS subsystems of a wireless communications network.
2. Description of Related Art
Determination of the precise geographic location of a wireless device, such as a cellular phone or personal communications services (PCS) device for example, is a capability that is now being developed and standardized for today""s PCS, cellular and satellite based wireless networks. Deployment of this capability is required, for example, in the US to fulfill the FCC""s phase 2 requirements for E911 calls. Known strategies to obtain a geographic location typically employ either (a) an overlay solution in which the entities that perform location measurement and location computation are external to the wireless communications network and communicate using external or externally available transmission and switching capabilities or (b) an integrated solution in which these entities form part of the wireless network and make use of communication capabilities provided within the network.
A typical terrestrial wireless communications network (for example cellular or PCS) consists of three major subsystems: the Base Station Subsystem (BSS), Network SubSystem (NSS) and Operations and Maintenance Subsystem (OMS). Wireless communication networks are typically categorized into xe2x80x9cgenerationsxe2x80x9d according to the technology being implemented. For example, the generation of a particular wireless technology is now commonly accepted in the art with first generation corresponding to systems supporting an analog radio interface (e.g. AMPS), second generation supporting a digital radio interface with a peak bit rate for any application of around 64 kbps (e.g. GSM, PCS1900, CDMA IS-95, TDMA) and third generation supporting a peak bit rate for applications of at least 384 kbps (e.g. CDMA2000, WCDMA).
In many existing first and second generation wireless technologies (e.g. GSM, CDMA IS-95, TDMA, AMPS), the BSS includes logically or physically distinct entities to serve as a Base Station Controller (BSC), Base Station Transceiver Station (BTS) and a Transcoding and Rate Adaptation Unit (TRAU). Logically distinct units may be physically supported on a common hardware platform while retaining their distinct functions. The NSS contains logically or physically distinct entities to serve as a Mobile Switching Center (MSC), Visitor Location Register (VLR), Home Location Register (HLR), Authentication Center (AC), Equipment Identification Register (EIR). The functions of these different entities are known to those of ordinary skill in the art of wireless networks. In simple terms, the BSS manages the radio aspects of the network whereas the NSS manages mobility, call control and supplementary services (e.g. call forwarding, short message service). For second generation systems supporting packet data communicationxe2x80x94e.g. General Packet Radio Service (GPRS)xe2x80x94other entities are included in the NSS such a Serving GPRS Support Node (SGSN) and Gateway GPRS Support Node (GGSN). For third generation systems, entities are further modified and/or new ones are introduced in the NSS and BSS. The constituents of the BSS and NSS for third generation systems are subject to future developments in technology and standards.
Typical models of a geographic location service in a wireless network (e.g. as being deployed for FCC E911 phase 2) assume that some external user, sometimes termed a xe2x80x9cclientxe2x80x9d, interacts with the wireless network to obtain the geographic location of a Wireless Mobile Subscriber (MS, or xe2x80x9cwireless devicexe2x80x9d) either on demand or when some predetermined event occurs (e.g. the origination of an E911 call). The wireless network then instigates the procedures that will lead to a geographic location estimate for the particular MS.
In order to obtain an accurate geographic location for an MS, radio related measurements must generally be taken involving either (or in some cases both of) the uplink radio transmission from the MS or (and) downlink radio transmission to the MS. The resulting measurements, normally made over a short time period (e.g. a few milliseconds to a few seconds), then form the input to a computational algorithm from which a geographic position (e.g. latitude and longitude coordinates) is produced.
Examples of existing positioning methods include Time Of Arrival (TOA), Time Difference Of Arrival (TDOA), Angle of Arrival (AOA), Timing Advance (TA), Observed Time Difference (OTD), Enhanced Observed Time Difference (EOTD), Observed Time Difference Of Arrival (OTDOA), Global Positioning System (GPS). These methods can be allocated among the following categories (in some cases with different variants of the same method appearing in more than one category):
(a) Network Based (e.g. TOA, TDOA, TA, AOA)xe2x80x94measurements of uplink MS radio transmissions are made by the network with position computation in the network.
(b) Mobile Assisted (e.g. OTD, E-OTD, OTDOA, GPS)xe2x80x94measurements of downlink radio transmission (emanating from the wireless network or from other sources like GPS satellites) are made by the MS. These measurements are then provided to the network where position computation occurs.
(c) Mobile Based (e.g. OTD, E-OTD, OTDOA, GPS)xe2x80x94measurements of downlink radio transmission (emanating from the wireless network or from other sources like GPS satellites) are made by the MS. Position computation using these measurements is then also performed by the MS.
In order to support the above categories, two special functional entities are required in addition to those already existing in the wireless network and MS: a location measurement entity (LME) to perform radio related measurements and a location computation entity (LCE) to compute a geographic location estimate from the measurements provided by the LMEs. These terms are generic and correspond to certain more specific entities in particular wireless technologies. Thus, for example, the LCE can correspond to both the Positioning Determining Entity (PDE) used in ANSI-41 based networks (e.g. TDMA, CDMA IS-95) and the Serving Mobile Location Center (SMLC) defined for GSM and PCS1900 networks. Similarly, the LME can correspond to the radio elements of a Positioning Determining Entity (PDE) in ANSI-41 networks and to the Location Measurement Unit (LMU) defined for PCS1900 and GSM networks. Further, the LME typically may be accessed using only wireline facilities or may be accessed by wireline and wireless means (e.g. RF, microwave) including wireless access similar to or the same as that supported for normal MSs within the wireless network.
One known architectural solution for communicating geographic location information between the LCE and the LME and/or MS is known as an xe2x80x9cNSS solutionxe2x80x9d. The LCE is typically attached and directly accessible only to the NSS. Disadvantageously, this architecture relies on the NSS to support signaling between the LCE and both the LME and MS. Thus, any hardware and/or software limitations and failures in the NSS can negatively impact the timely and accurate flow of information. There may also be signaling limitations in the NSS that restrict the volume of data that can be transferred between an LCE and an LME and between an LCE and an MS per unit of time, resulting in a limitation on the number of location attempts that can be performed per unit of time. This limitation may also produce increased delay for location attempts that do succeed due to the extra signaling delays in the NSS plus any queuing delay when signaling throughput limits are reached. An example of a location application for which these limitations may be significant is xe2x80x9chome zone billingxe2x80x9dxe2x80x94a service in which an MS subscriber is billed at a special (e.g. flat or reduced) rate when making or receiving calls within a predefined home zone area. To verify whether the MS actually is within the home zone area, a wireless network would need to perform at least one location determination for every incoming and outgoing call and possibly additional location determinations at periodic intervals during a call or when a call is handed over from one BSS cell site to another. Such a service implies several location determinations per subscriber per hour during peak busy periods. The ensuing signaling load in the NSS would then be heavy particularly if a network based positioning method was being used where several LMEs need to send measurements related to the location of the MS through the NSS to the LCE for each attempt to locate an MS.
Another known architectural solution for communicating geographic location information between the LCE and the LME and/or MS is known as a xe2x80x9cBSS variantxe2x80x9d or xe2x80x9cBSS solutionxe2x80x9d. The LCE is typically attached and directly accessible only to the BSS. LME to LCE signaling (to transfer measurements from the LMEs to the LCE) and LCE to MS signaling (to support mobile based and mobile assisted position methods) are then both supported by signaling facilities in the BSS only. Disadvantageously, access by the NSS to the LCE (e.g. to initiate a location procedure and receive the resulting location estimate) needs to go through intermediate signaling facilities in the BSSxe2x80x94i.e. is less direct than with an NSS solution. This can negatively impact the timely and accurate flow of information that enable access to the LCE from the NSS for any location application in which the client is supported within or by the NSS.
It is an object of the invention to provide a hybrid system and method for determining the location of a wireless device.
It is another object of the invention to provide a system and method for determining the location of a wireless device with fewer throughput limitations and delays than known NSS solutions.
It is another object of the invention to provide a system and method for determining the location of a wireless device while avoiding some throughput limitations and delays of known BSS solutions.
The present invention is applicable to both an integrated and overlay solution. A hybrid system and method of location determination is utilized in which the location determination functionality is provided in part by the BSS and in part by the NSS. Advantageously, the division of functionality among the BSS and NSS can reduce network infrastructure impacts and improve performance compared to either a pure BSS or pure NSS approach.
With the hybrid architecture, LME to LCE signaling does not rely on signaling capability in the NSS and does not overburden the signaling facilities in the NSS. Although in a preferred embodiment MS to LCE signaling still relies on signaling facilities in the BSS and NSS, as in the NSS based architecture, the volume of such signaling will be substantially zero for network based positioning methods (where there is no MS to LCE signaling). With regard to the MS based or MS assisted positioning support by the hybrid architecture, while there is additional signaling through the NSS to support MS to LCE signaling, in a preferred embodiment there is no extra signaling through the BSS to enable access to the LCE from the NSS. Advantageously, software and/or hardware impacts in the BSS are not needed to support NSS access to the LCE.
The hybrid location services architecture can support location of MS subscribers in a wireless network and can be used in conjunction with any network based, mobile assisted and mobile based position methods.